<table>
  <thead>
    <tr>
      <th></th>
      <th v-for="c in cols">{{ c }}</th>
    </tr>
  </thead>
  <tbody>
    <tr v-for="i in cells[0].length">
      <th>{{ i - 1 }}</th>
      <td v-for="(c, j) in cols">
        <Cell :r="i - 1" :c="j"></Cell>
      </td>
    </tr>
  </tbody>
</table>
